The present invention relates to an liquid crystal display device. More specifically, the invention relates to a back light unit for a liquid crystal display panel.
A liquid crystal display panel is comprised the pair of opposed substrates and a liquid crystal layer interposed between the pair of substrates, wherein an array of pixels is formed in a horizontal plane of the liquid crystal display panel. In this case, a back light unit is needed, and such a back light unit is arranged in the back of the liquid crystal display panel. Thus, each pixel has only the function to control the amount of light switching by controlling the orientation of the liquid crystal molecules.
This back light includes a lamp tube, a diffusing plate and a reflector for supplying the light and uniformalizing the light irradiation of a liquid crystal display panel. A cold cathode fluorescent tube (CFL), whose length is almost equal to the length in a parallel direction of the liquid crystal display panel and which is supplied with a voltage by electrodes attached at both ends of the tube, is used as the lamp tube.
However, a liquid crystal display unit's life span is determined by a lamp tube's short life span. Although replacement of the lamp tube in the back light unit is not easy, all lamps should be replaced to maintain the brightness of the back light unit.
In addition, an electrode material inside the cold cathode fluorescent tube tends to adhere on the inner wall of the lamp tube due to sputtering which occurs while lighting, and so the lamp tube tends to become dark more and more due to the adhesion materials over time. That is, the adhesion materials become an alloy (amalgam) of the mercury inside the cold cathode fluorescent tube, and so the lamp tube's life span shortens more and more by consuming mercury.